i have the same concerns for losing low-end power (if that's what you meant). i have friends who put bolt-on "performance" parts on their cars. although they gained high-end torque they lost low-end. they have cars or sports cars so maybe it's ok for them but that's the complete opposite of what i want for my xterra. i couldn't care less about high-end power, as i tend to baby my gas pedal anyways.